1. Field of the Invention
The present invention relates to a superconducting fiber or filament having superconducting property and a method for preparing the same.
2. Description of the Related Art
The superconductivity is a phenomenon which is explained to be a phenomenon of a kind of phase change of electrons under which the electrical resistance become zero and the perfect diamagnetism is observed. Thus, a variety of application of the superconductor have been proposed in every field.
Zero resistance which is the most important property of the superconductor can be advantageously utilized in a magnetic coil, a magnet in addition to a power cable. However, the critical temperature of the superconductors could not exceed 23.2K of Nb.sub.3 Ge which was the highest Tc for the past ten years.
The possibility of an existence of new types of superconducting materials having much higher Tc was revealed by Bednorz and Muller, who discovered a new oxide type superconductor in 1986 [Z. Phys. B64 (1986)189]
It was also reported that C. W. Chu et al. discovered, in the United States of America, another superconducting material so called YBCO type represented by YBa.sub.2 Cu.sub.3 O.sub.7-x having the critical temperature of in the order of 90K in February 1987. Still other type new superconducting materials which were reported recently are a compound oxide of Bi-Sr-Ca-Cu-O system and Tl-Ba-Ca-Cu-O system which exhibit such high Tc as more than 100K and which are chemically much stable than the abovementioned YBCO type compound oxide.
And hence, the application of the high-temperature superconductors will be enlarged remarkably.
These new type superconducting materials are, however, ceramic materials are produced by a sintering technique in which a compact of powder material is sintered in a furnace, so that they can not or are difficult to be shaped into a shape of wire or tape which can be used in practical uses.
Taking the abovementioned situation into consideration, the present inventors have proposed a process for manufacturing a ceramic wire in the following U.S. patent applications: Ser. No. 152,713 filed on Feb. 5, 1988, Ser. No. 161,480 filed on Feb. 29, 1988, Ser. No. 182,489 filed on Apr. 18, 1988, Ser. No. 189,366 filed on May 2, 1988, Ser. No. 225,207 filed on July 28, 1988 or the like.
The above-mentioned compound oxide type superconductors possess an anisotropy property in their superconducting properties. It is known that the critical current density increase remarkably when the crystalline orientation in the compound oxides is correctly ordered. However, it is difficult to realize such high ordering of crystalline structure in sintered products. In fact, no particular control have not effected in the abovementioned superconducting wires produced by the sintering technique.
An object of the present invention is to overcome the abovementioned problems of the conventional technique and to provide a new concept of superconducting fiber or filament and a process for producing the same.